ssssoygo

SELECT 
    t.ID, 
    ADD_MONTHS(t.Дата_начала, LEVEL - 1) AS Дата, 
    t."Кол-во"
FROM 
    your_table t
CONNECT BY 
    LEVEL <= t."Кол-во" + 1
    AND PRIOR t.ID = t.ID
    AND PRIOR sys_guid() IS NOT NULL
START WITH 
    1 = 1
ORDER BY 
    t.ID, Дата;